Recently, the development of two-terminal nonvolatile resistance change elements such as a ReRAM (Resistive Random Access Memory) is being extensively performed. This nonvolatile resistance change element can perform a low-voltage operation and high-speed switching and can be downsized, and hence is a leading candidate for a next-generation, large-capacity memory device that replaces a floating gate type NAND flash memory. In particular, a nonvolatile resistance charge element using amorphous silicon as a resistance change layer is promising from the viewpoints of a low-current operation, the data retention, the endurance, and downsizing.
A memory having a cross-point structure has been proposed as a large-capacity memory device using this nonvolatile resistance change element as a memory cell. In this cross-point memory, a sneak current that sneaks to an unselected cell is generated when performing write, read, or erase to a selected cell.
If this sneak current is generated, the power consumption increases in a large-capacity memory device, and write and erase to a selected cell become difficult. In addition, an array itself can no longer function because the increase in electric current causes disconnection of an interconnection or the like. In the cross-point structure, therefore, the two-terminal nonvolatile resistance change element must be given a rectifying function by combining a diode.
Unfortunately, combining the nonvolatile resistance change element and a diode increases the element size, and this makes integration difficult. To solve these problems, a nonvolatile resistance change element with a rectifying function is necessary, and demands have presently arisen for the development of the element.
The nonvolatile resistance change element includes a resistance change layer, a metal electrode, and a semiconductor layer as a counterelectrode for the metal electrode. A conductive filament growing from the metal electrode is shortcircuited to the counterelectrode and restored in the metal electrode, thereby changing the resistance between the electrodes and achieving switching characteristics. In this resistance change element, the conductive filament comes in direct contact with the semiconductor layer. Therefore, a chemical reaction in the interface may change the Schottky characteristics, or the diffusion of the conductive filament (a metal) to the semiconductor layer may form recombination centers and vary an electric current, i.e., the device characteristics may vary.